Forces in A Structure

I've been toying around with West-Point Bridge Designer and wondering how it does it's calculations. If you have a simple structure like the image below, how do you analyze the forces on each member (assume all triangles are equilangular and equilateral)? I'd imagine it's all vectors, but I'm not sure about anything beyond that. Could someone link me in the right direction, or diagram the forces?

First of all you have to define how the structure is supported. Your drawing does not show any support. Is the structure flying in the space?. When you clear how is supported I will give you some hints for the resolution, because it depends on the structure force reactions.